This invention pertains to monitoring the speed and travel of a moving article, such as a moving sheet of veneer, without contacting the article. For the purpose of illustration herein, a preferred embodiment of, and a preferred method of practicing, the invention are described in conjunction with the clipping of veneer, in which application the invention has been found to have particular utility.
There are many applications where it is desirable to be capable of monitoring, continuously and accurately, the speed and/or travel distance of a moving article without contacting the article. While various approaches to this problem have been made in the past, the present invention is believed to be grounded on a significantly improved approach, whereby the accuracy and reliability of derived speed and travel distance information are appreciably superior to what has been obtainable heretofore.
Thus, a general object of the present invention is to provide a unique method and apparatus for the noncontact monitoring of the speed and travel of a moving article, which method and apparatus yield extremely accurate and reliable information.
Another object of the invention is to provide such a method and apparatus which is usable in a wide variety of applications and environments, and which does not require the services of skilled personnel.
A further object of the invention is to provide a method and apparatus as indicated which is capable of following even minute changes in the instantaneous speed of an article, and in the actual distance which the article covers in a given unit of time.
Yet another object of the invention is to provide apparatus of the type generally indicated which is extremely simple in construction, and readily mountable for use in numerous ways without requiring any appreciable modification of adjacent equipment.
The novel method of the invention contemplates the viewing of a moving article, and the production from such viewing of a unidirectionally defocused image of the article, which image comprises elongated substantially parallel moving bands of light. The method further contemplates the projection of such an image onto a photodetector, and the generation by the photodetector of an AC electrical signal whose frequency is at all times directly proportional to the then speed of the moving bands, and hence directly proportional to the speed of the viewed article. Another important characteristic of this signal is that a count of its cycles during an interval yields a direct indication of the actual travel distance covered by the article during such interval.
According to a preferred embodiment of the invention, the proposed apparatus comprises an optical viewing and imaging system, which includes spaced, coaxial, positive lenses that cooperate with a cylindrical lens to produce an image of the type just generally described above. These positive lenses include what might be called a "front" or "viewing" lens, and a "rear" or "imaging" lens--the nodal point of the latter being located, according to the invention, at the focal point of the former. Also included in the apparatus is a photodetector onto which an image produced by the imaging system is projected for the purpose of generating an electrical signal containing the desired speed and travel information. While several different specific photodetectors are illustrated and described herein, in general terms each comprises a plurality of elongated, substantially parallel, laterally spaced, side-by-side adjacent light-sensitive surfaces. The photodetector and imaging system in the apparatus are so oriented with respect to one another, that the longitudinal axes of the bands of light in an image derived from viewing a moving article substantially parallel the longitudinal axes of the light-sensitive surfaces in the photodetector. Reasons for the significance of such an arrangement will be discussed later.
With the construction just outlined, several important advantages are attained. For example, with the imaging system including a pair of spaced coaxial positive lenses, positioned as indicated, changes in the distance between a viewed article and the apparatus, within a predetermined range of distances, do not appreciably affect the appearance of the image produced by the imaging system. Thus, close tolerances are not involved with respect to mounting of the apparatus in place; and, slight movements of an article toward and away from the apparatus as the article travels through the field of view of the imaging system also do not affect image appearance. This latter consideration is of large importance in contributing toward maximum accuracy respecting the measurements made by the apparatus, since, if slight distance changes between an article and the apparatus could appreciably affect image appearance, they would also (as will become apparent) significantly affect the reported speed and travel distance of the article.
A further notable feature of the proposed imaging system is the incorporation therein of a cylindrical lens, or the like, which produces unidirectional defocusing in an image, whereby the projected image appears as elongated parallel bands of light. Suffice it to say, at this point, that the use of such a lens to produce such a defocused image both greatly improves the accuracy of the apparatus, and greatly simplifies its construction. The reasons for this will be explained more fully below.
Various other objects and advantages attained by the invention, including particular advantages offered by several different photodetector constructions disclosed herein, will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings.